(1) Field of the Invention
The present invention relates to an alloy steel powder having excellent compressibility and moldability and further having excellent heat-treatment properties, that is, carburizing property and hardenability in its sintered steel or powder forged steel, which powder is used in the production of machine structural parts through the powder metallurgy.
In general, in the powder metallurgy, raw material steel powder is press molded to produce a green compact, the green compact is sintered and heat treated, and further the sintered body is subjected to coining, forging, heat-treatment, and occasionally cutting to produce a final product having a higher density and a higher strength.
Therefore, the raw material steel powder is demanded to have the following properties. When a green compact is produced by a press molding of the raw material steel powder, the steel powder must be excellent in the compressibility and moldability. While, in order to give a mechanical strength to the sintered steel or powder forged steel through sintering and heat-treatment, the sintered steel or powder forged steel must be excellent in the heat-treatment properties, such as sinterability, uniform texture-formable property, carburizing property, nitriding property, hardenability and the like, and when the sintered body is subjected to a mechanical working, the sintered body must be excellent in the machinability. The present invention relates to an alloy steel powder which satisfies the above described demands in the use as a raw material powder for the production of alloy steel for machine structural parts.
(2) Description of the Prior Art
There have recently been developed various technics for strengthening the materials for iron series sintered machine parts produced from various alloy steel powder through the powder metallurgy, for example, a technic for producing alloy steel powder by the water-spray method, a technic for deoxidizing and annealing water-hardened unannealed steel powder, and the like. Such machine part is, for example, engine part, which is required to have high heat-resistance, abrasion resistance and oxidation resistance. Further, there has been developed a technic for producing large size machine parts, wherein pure iron powder used as a main raw material is mixed with various metal and non-metal powders, such as graphite powder, cobalt powder, nickel powder and other metal powder and alloy powder thereof, the resulting mixture is sintered to produce a machine part, and the machine part is subjected to heat-treatment, such as carburization hardening and the like. The inventors have made various investigations in order to meet these demands and accomplished the present invention.